Protein expression during heat stress in thermo-intolerant and thermo-tolerant diatoms

Diatoms (Chrysophyta) are photosynthetic microorganisms that are abundant in the natural environment and often associated with specific habitat and water quality conditions. Their significance as bioindicators and as exploitable sources of fine chemicals makes them desirable candidates for the study of stress responses. The protein expression of a thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) diatom following exposure to elevated temperature was investigated using one- and two-dimensional gel electrophoresis and Western blot analysis. It was determined using SDS PAGE with ³⁵S-methionine labeled proteins and Western blot analysis using pea HSP70 antisera that higher temperatures and longer duration treatment were required to cause a noticeable stress response in C. muelleri compared to P. tricornutum. This may be explained by C. muelleri possessing higher amounts of constitutively expressed heat shock proteins, which allows these cells to rapidly adjust to temperature increases. Two-dimensional gel electrophoresis revealed that putative small heat shock proteins (smHSPs) may appear to play a role during heat stress in both diatoms, which is similar to the response in plants. SDS PAGE data are also presented characterizing the recovery of P. tricornutum after heat shock. These results suggest that there is a lag period between heat shock and stress protein synthesis in these thermo-intolerant cells. This supports the hypothesis that cells without higher amounts of constitutively expressed stress proteins have a greater sensitivity to increased temperature. Work is underway to identify particular stress proteins responsible for conveying thermo-tolerance and to determine if overexpression of these genes in thermo-intolerant diatoms affects their temperature sensitivity.